GaN-based materials, including InGaN, GaN and AlGaN alloys, are direct gap semiconductors with band gap continuously adjustable from 1.8 to 6.2 eV. Thanks to wide direct gap, strong chemical bond and resistance to high temperature and corrosion, GaN-based materials are ideal for producing light-emitting devices with short wavelengths and high luminance, and are widely applied in fields like full color screen display, LCD backlight source, signal light and lighting.